#include <stdio.h>
int binarySearch(int arr[], int, int, int); 
int exponentialSearch(int arr[], int n, int x) 
{ 
    // If x is present at firt location itself 
    if (arr[0] == x) 
        return 0; 
  
    // Find range for binary search by 
    // repeated doubling 
    int i = 1; 
    while (i < n && arr[i] <= x) 
        i = i*2; 
  
    //  Call binary search for the found range. 
    return binarySearch(arr, i/2, min(i, n), x); 
} 
  
// A recursive binary search function. It returns 
// location of x in  given array arr[l..r] is 
// present, otherwise -1 
int binarySearch(int arr[], int l, int r, int x) 
{ 
    if (r >= l) 
    { 
        int mid = l + (r - l)/2; 
  
        // If the element is present at the middle 
        // itself 
        if (arr[mid] == x) 
            return mid; 
  
        // If element is smaller than mid, then it 
        // can only be present n left subarray 
        if (arr[mid] > x) 
            return binarySearch(arr, l, mid-1, x); 
  
        // Else the element can only be present 
        // in right subarray 
        return binarySearch(arr, mid+1, r, x); 
    } 
  
    // We reach here when element is not present 
    // in array 
    return -1; 
} 
  
// Driver code 
int main(void) 
{ 
   int arr[] = {2, 3, 4, 10, 40}; 
   int n = sizeof(arr)/ sizeof(arr[0]); 
   int x = 10; 
   int result = exponentialSearch(arr, n, x); 
   (result == -1)? printf("Element is not present in array") 
                 : printf("Element is present at index %d", 
                                                    result); 
   return 0; 
} 